Field of the Invention
The present invention generally relates to ignition devices and, more particularly, photo-ignition devices.
Description of the Related Art
Ignition in propulsion systems is established by a number of different methods, most often through one of many electrical ignition devices. In liquid-fueled systems, for example, plasma torches may be employed. Alternatively, electric spark plugs may be used to initiate a gas burning torch. In many cases, relatively heavy components may need to be employed. And, many of these ignition systems may further require additional gas/fuel tanks, pumps, values, and parts, each of which may introduce reliability issues.
Different categories of propulsion systems may have different ignition requirements. For liquid-fueled propulsion systems, where electrical ignition is often employed, fuel and oxidizer must be effectively mixed in proper proportions to have a controlled rate of production of hot gases. A “hard start” in one of these systems indicates that a quantity of combustible propellant that entered a combustion chamber prior to ignition was too high, preventing the ignition system from establishing complete combustion throughout the combustion chamber. The result is generally an excessive spike of pressure, possibly leading to structural failure or even potentially an explosion. These and other conventional methods of ignition may also have issues associated with flame propagation and the combustion wave. They may rely on propagation of ignition through booster charges or pyrophoric materials in order to establish ignition in a combustion chamber (with the exception of hypergolic ignition), which may also contribute to “hard start” conditions.
In electric ignition systems, conductive wires connect explosive material to an electric source, which may require protection against electrostatic discharge (ESD) to avoid unintentional firing. However, use of ESD protection devices may introduce reliability issues into the system. Alternatively, another category of electric ignition employs a low voltage electrical current to generate heat for ignition instead of a spark. For example, many solid-fueled propulsion systems are usually ignited with one-shot pyrotechnic devices, generally including different forms of explosive bags and pellet baskets. These systems are typically initiated by an electric ignition source, often a resistive wire, generally known as an “electric match.” Upon receiving an electrical signal, the initiator ignites a small solid pyrotechnic, generally known as a squib or primer charge. Then, a booster charge is ignited by heat released by the squib, which in turn ignites the main propellants within a fraction of a second. However, such systems may suffer from slow starts, as well as problems similar to ESD systems. In multigrain systems, pressurization of void volume and creation of a desirable delay between successive stages may present additional challenges.
Some liquid fuel/oxidizer combinations ignite on contact (hypergolic). Other non-hypergolic fuels may be “chemically ignited” by priming fuel lines with hypergolic propellants. In these systems, the chemical ignitions may present corrosiveness, toxicity, and reliability issues. Additionally, there may are also be issues associated with timely ignition and propagation of flame throughout a sizable combustion chamber, which becomes more of a challenging issue for larger engines.
An alternative to the above ignition categories is laser ignition. Laser ignition is typically used for ground-based initiators and it is usually external to the flying propulsion systems or spacecrafts, due to its heavy weight and high power consumption. In this approach, an external laser shoots a high power beam of light into a combustion chamber for a one-shot ignition. The lack of any electrical contacts with the ignitable material is one of the advantages of laser ignition, thus eliminating hazards identified above including associated electrostatic discharge (ESD). However, laser ignition is less common in typical propulsion systems, because it requires a relatively powerful laser that is bulky and costly in addition to the high power requirement.
Accordingly, there is a need in the art for low energy, portable ignition technologies that satisfy the numerous requirements while maintaining simplicity.